Reliability Assessment of Steel Bridges for Specialized Hauling Vehicles

Abstract

Specialized hauling vehicles (SHVs) are short heavy trucks within the legal weight limits but induce higher load effects than routine commercial loads. The Manual for Bridge Evaluation (MBE) adopted a series of single-unit trucks (SUs) to represent this type of vehicle. However, the SUs were introduced without rigorous reliability-based analysis due to the lack of data on SHVs. With the availability of vast amounts of data on weigh-in-motion (WIM) truck weights and configurations, the reliability of steel bridges under the SHVs should be evaluated in a more robust and quantitative manner. Through the utilization of WIM data, the authors quantified the SHVs in terms of percentages of SHVs among all truck traffic, daily average counts of SHVs, and number of axles. The gross vehicle weights (GVWs) and typical configurations of SHVs were investigated. In addition, their load effects were determined and normalized by the corresponding SUs. The maximum live loads corresponding to a return period of 5 years were also extrapolated using normal probability paper (NPP). To evaluate the effectiveness of current load-rating procedures for SHVs, the authors investigated the relationship between the load-rating factors and the corresponding reliability indices for existing bridges using the developed live load parameters based on the WIM data. Results indicated that the current live load factors were not able to provide a uniform and appropriate reliability index at different average daily truck traffic (ADTT) scenarios. This paper thus proposes new live load factors and weight adjustments of SU trucks to provide an adequate and uniform safety margin for the evaluation of steel bridges.

Impact of Specialized Hauling Vehicles and Emergency Vehicles on Bridge Load Rating

“…The rating factors presented in Equations 3 and 4 can be further improved by using the adjusted live load factors, as proposed by Lou et al ( 7 ) and by this study. By implementing the adjusted live load factors, the conversion equation are updated with a adjustment factor that is result from decreased live load factor.…”

“…In 2011, NCHRP Project 12-78 ( 6 ) prescribed live load factors for SHVs which are essentially the same as the AASHTO routine commercial traffic. Lou et al ( 7 ) recommended reliability-based live load factors of SUs for the U.S. and New Jersey based on the nation-wide and state-wide weight-in-motion (WIM) data, respectively.…”

“… Note : ADTT = average daily truck traffic; SU = single unit; EV = emergency vehicle; FAST Act = Fixing America’s Surface Transportation Act. a Based on the recommended national live load factors proposed by Lou et al ( 7 ). …”

Reliability-Based Assessment of Concrete Decks Designed Using Approximate Method at the Strength I Limit State

“…For example, the traversing of the emergency vehicles, which are exempted from the Federal Bridge Formula B, contributes to both heavy single axles and heavy tandem axle ( 7 ). Moreover, with the growing popularity of specialized hauling vehicles tridem axles are becoming more common, whose load effects have not been evaluated thoroughly ( 8 ). The tridem axles could result in heavier load effects than the single and tandem axles, whereas they are not reflected in the current design loads.…”